UNIVERSITY   OF   CALIFORNIA 

COLLEGE    OF    AGRICULTURE 
AGRICULTURAL   EXPERIMENT  STATION 

CIRCULAR  No.  228 
June,  1921 

VINEYARD  IRRIGATION  IN  ARID  CLIMATES 

By  FEEDERIC  T.  BIOLETTI 


There  is  much  difference  of  opinion  among  grape  growers  in  the 
Imperial  Valley  and  similar  regions  as  to  the  number,  time,  and 
volume  of  irrigations  needed.  Undoubtedly  the  main  cause  of  this 
difference  is  the  variation  in  character  of  the  soils  in  which  vines  are 
growing. 

What  is  the  best  way  to  irrigate  vines  in  these  regions?  There 
is  no  single  correct  answer  to  this  question.  Each  case  is  a  special 
problem.  To  arrive  at  a  satisfactory  solution  we  must  know  (a)  the 
water  requirements  of  the  vines  and  (&)  the  reaction  of  the  particular 
soil  to  the  water  we  apply ;  that  is,  how  the  water  applied  to  the  soil 
is  absorbed,  distributed,  and  lost. 

Water  Requirements  of  the  Vine. — In  winter,  the  vine  is  dormant 
and  is  then  comparatively  indifferent  to  the  water  content  of  the  soil. 
So  long  as  the  soil  is  moderately  moist  around  most  of  its  roots  it 
will  not  suffer  from  drought.  On  the  other  hand,  it  is  equally  re- 
sistant to  excess  of  water  at  this  time.  When  the  vines  are  dormant, 
the  vineyard  may  be  flooded  and  the  roots  may  stand  in  saturated 
soil  for  several  weeks  without  injury.  (Warning:  The  last  remark 
does  not  apply  to  young  vines  just  planted.  Nursery  rootings  and, 
still  more,  cuttings,  are  very  sensitive  to  excess  of  water  and  a  few 
days  in  saturated  soil  may  cause  them  to  decay.  It  is  only  after  they 
have  made  a  year's  growth  and  have  an  established  root  system  that 
they  acquire  resistance  to  standing  water.  On  the  other  hand,  they 
are  as  resistant  to  dryness  as  are  established  vines.) 

As  soon  as  the  activities  of  the  vine  are  aroused  by  the  warm 
weather  of  spring,  it  loses  its  indifference  to  the  water  content  of 
the  soil.  When  the  new  rootlets  start,  they  quickly  decay  if  the 
soil  is  so  saturated  with  water  that  all  air  is  excluded.  Also  when 
the  buds  start  and  produce  leaves,  these  soon  stop  growing  and  wither 
if  the  soil  moisture  supply  does  not  remain  adequate  for  the  young 
rootlets. 

From  this  time  until  the  harvesting  of  the  crop,  the  vines  will 
do  their  best  only  if  the  young  feeding  roots  are  growing  in  soil 


containing  all  the  water  they  can  nse  but  not  so  much  as  to  exclude 
the  air  which  they  equally  need.  To  determine  this  optimum  degree 
of  moisture  requires  observation  and  experience.  Occasional  borings 
with  a  soil  auger  should  be  made  to  at  least  four  feet  until  experience 
has  determined  what  is  the  best  way  of  irrigating  to  get  the  required 
condition.  If  the  water  does  not  penetrate  so  deep  as  the  roots,  more 
irrigation  is  needed.  If  the  soil  at  four  feet  or  less  remains  muddy 
over  48  hours  after  irrigation,  less  should  be  applied. 

The  problem  is  relatively  simple  in  deep  soils  which  take  water 
easily  and  where  the  drainage  is  good.  In  such  soils  there  is  little 
danger  of  over-irrigation.  On  the  other  hand,  in  shallow  soils,  that  is, 
soils  underlaid  by  impervious  layers  at  four  feet  or  less,  the  problem 
is  often  difficult. 

In  the  first  instance,  one  or  two  heavy  irrigations  early  in  the 
season  followed  by  proper  cultivation  to  prevent  weed  growth  and 
excessive  surface  evaporation  may  be  sufficient  to  provide  the  needed 
moisture  conditions.  In  the  second,  a  heavy  irrigation  is  safe  only 
in  the  winter  while  the  vines  are  completely  dormant.  During  the 
growing  season,  the  vines  must  be  supplied  with  the  required  moisture 
by  frequent  light  irrigations  and  care  taken  to  keep  all  the  soil  con- 
taining roots  moist  without  being  muddy.  In  such  soils  a  number  of 
two-inch  test  holes  six  feet  deep  supplied  with  a  two-inch  perforated 
iron  pipe  are  useful  as  a  means  of  determining  the  level  of  saturated 
soil.  They  should  be  placed  in  various  parts  of  the  vineyard, 
especially  where  the  ground  is  lowest,  and  will  do  much  to  simplify 
the  problem  of  applying  sufficient  water  without  danger  of  water- 
logging the  soil.  Frequent  use  of  a  soil  auger  is  also  advisable  as  a 
means  of  testing  the  moisture  conditions. 

Up  to  the  harvest  season,  the  water  requirements  of  the  vine  are 
at  their  maximum.  Water  is  required  for  new  growth,  for  the  devel- 
opment and  maturing  of  the  crop,  and  for  the  abundant  foliage  on 
which  both  of  these  activities  depend. 

After  the  harvest  the  requirements  are  less.  All  that  is  needed 
is  sufficient  moisture  to  keep  the  leaves  in  good  working  condition 
without  promoting  new  growth.  It  is  the  work  of  the  leaves  after 
the  crop  is  harvested  that  matures  the  canes  and  lays  up  the  reserve 
stores  of  nutriment  in  the  buds  and  other  parts  of  the  vine  on  which 
the  healthy  growth  and  crop  of  the  following  year  largely  depend. 
Too  much  water  at  this  period  is  dangerous  as  it  may  stimulate  con- 
tinued development  and  growth  of  new  shoots  instead  of  properly 
maturing  the  canes  and  buds  already  formed. 

Absorption,  Distribution,  and  Loss  of  Water. — In  order  to  satisfy 
the  requirements  of  the  vine  the  water  must  be  applied  differently, 
according  to  the  nature  of  the  soil. 


If  the  soil  is  pervious,  the  water  must  be  run  in  short  furrows  or 
small  checks  and  with  a  relatively  large  * '  head. ' '  Otherwise  the  land 
near  the  head  of  irrigation  will  receive  too  much  and  that  at  the  other 
end  too  little.  If  the  soil  takes  water  slowly,  the  furrows  may  be 
longer  and  the  time  of  irrigation  must  be  longer,  to  permit  the  water 
to  penetrate  to  the  required  depth.  If  the  soil  is  shallow,  irrigations 
must  be  more  frequent  to  keep  a  sufficient  supply  of  water  available 
to  the  vines  at  all  times.  In  soils  where  water  percolates  down- 
ward more  rapidly  than  horizontally,  the  irrigating  furrows  should 
be  close. 

The  water  which  gets  into  the  soil  disappears  by  transpiration 
through  the  leaves  of  the  vines,  through  weeds,  and  through  inter- 
crops, by  evaporation  from  the  surface  of  the  soil,  and  by  draining 
through  the  subsoil.  The  more  leaf  growth  there  is,  therefore,  the 
more  water  is  needed ;  the  better  the  cultivation,  the  less  it  is  necessary 
to  apply,  and  the  better  the  drainage,  the  less  danger  there  is  of  over- 
irrigation. 

"With  so  many  factors  it  is  difficult  or  impossible  to  establish  definite 
rules.  The  best  method  can  be  determined  only  by  careful  trial  and 
observation  in  the  individual  case. 

Irrigation  the  First  Year. — Before  planting  a  vineyard,  the  soil 
should  be  wet  to  the  depth  that  the  roots  can  penetrate.  This  is  the 
main  irrigation  and  in  deep  soil  furnishes  a  supply  of  water  which 
is  available  to  the  vines  all  summer. 

This  preliminary  main  irrigation  is  essential  in  heavy  and  in 
shallow  soils.  In  deep  porous  soils  the  main  irrigation  may  be  given 
after  the  vines  are  planted,  but  in  relatively  impervious  soils  it  is 
difficult  to  give  the  large  volume  of  water  needed  without  danger  of 
causing  decay  of  young  vines  already  in  the  ground.  As  soon  as  the 
soil  works  well  after  this  irrigation,  and  before  it  becomes  dry,  the 
vines  may  be  planted. 

The  next  irrigation  should  be  given  soon  after  the  vines  have  made 
a  good  start  of  roots  and  shoots.  This  irrigation  should  be  light — 
sufficient  simply  to  replace  the  water  which  has  been  evaporated  from 
the  upper  soil.  It  is  best  applied  in  furrows  close  to  and  on  each 
side  of  the  vines.  Later  irrigations  should  be  applied  in  the  same 
way. 

Young  vines  require  comparatively  little  water.  If  the  soil  is 
kept  cultivated  sufficiently  to  prevent  weed  growth  little  is  lost  by 
evaporation  and  the  needs  of  the  vines  are  easily  met.  Cuttings  and 
rootings  will  form  roots  over  six  feet  long  the  first  season.  Too 
frequent  summer  irrigations  tend  to  promote  undesirable  surface 
roots. 


Late  irrigations  are  dangerous  with  young  non-bearing  vines. 
Late  irrigations  promote  late  growth,  which  often  fails  to  mature  or 
is  killed  by  frost.  A  large  growth  under  these  conditions  is  a  detri- 
ment. Large  vines  which  fail  to  mature  their  growth  make  less  growth 
the  following  year  than  small  vines  which  mature  their  wood  early. 

Irrigation  the  Second  Year. — The  irrigation  the  second  year  is 
similar  to  that  of  the  first.  The  main  irrigation  should  be  given 
towards  the  end  of  winter  before  the  vines  start,  providing  the  soil 
is  not  already  amply  supplied  with  moisture.  Later  irrigation^  should 
be  light  and  should  cease  in  time  to  allow  the  vine  to  mature  its  wood. 
The  danger  of  late  growth  is  even  greater  the  second  year  than  the 
first.  As  the  vines  now  have  a  widely  ramifying  root  system  extend- 
ing through  all  the  soil,  the  water  should  be  applied  to  all  parts  of 
the  vineyard  and  not  confined  to  furrows  close  to  the  vines. 

Only  in  shallow  or  very  open  soils  are  more  than  two  summer 
irrigations  needed.  In  most  cases,  the  last  irrigation  of  young,  non- 
bearing  vines  should  not  be  later  than  July.  When  intercrops  are 
grown,  more  water  must  be  used  to  supply  the  needs  of  the  inter- 
crop, but  in  such  a  way  that  the  intercrop  removes  the  extra  water. 
Weeds  may  sometimes  have  a  favorable  influence  by  removing  surplus 
water  during  the  late  summer. 

Irrigation  of  Bearing  Vines. — The  irrigation  of  bearing  vines 
should  in  general  follow  the  same  course.  The  production  of  a  crop, 
however,  makes  an  extra  demand  for  water.  In  many  cases,  a  supple- 
mentary summer  irrigation  a  little  before  the  grapes  ripen  is  advisable. 

Where  the  crop  is  harvested  early,  as  in  the  Imperial  Valley,  and 
especially  in  shallow  soils,  an  irrigation  after  the  removal  of  the  crop 
may  be  useful  or  even  necessary.  This  irrigation  should  be  sufficient 
to  keep  the  leaves  green  and  in  good  condition  until  the  weather  com- 
mences to  turn  cool  in  autumn,  but  not  sufficient  to  start  a  new 
growth  of  shoots.  A  gradual  yellowing  and  dropping  of  the  leaves 
from  a  diminishing  water  supply  in  November  and  early  December 
are  desirable. 

SUMMARY 

The  main  irrigation  and  the  wetting  of  the  subsoil  should  take 
place  when  the  vines  are  dormant. 

No  part  of  the  soil  should  remain  muddy  more  than  48  hours  while 
the  vines  are  growing. 

The  soil  should  become  sufficiently  dry  to  stop  new  growth  several 
weeks  before  the  arrival  of  cold  weather. 

Young,  non-bearing  vines  require  less  water  than  bearing  vines 
and  are  very  sensitive  to  injury  from  excess  of  water  soon  after  they 
are  planted,  and  from  cold  weather  or  frost  if  they  are  maturing  new 
growth  late  in  the  autumn. 


